Joel Smoller

Abstract:   In the early 1920’s theoretical astronomers came up with the so-called Standard Model of Cosmology, also called the FRW (Friedman-Robertson-Walker) spacetime. It was based on the so-called Cosmological, or Copernican, principle: the universe is homogenious (no preffered point), and isotropic (no preferred direction). In 1929, the American astronomer Edwin Hubble showed that the Universe is expanding: distant galaxies were receding from each other, and thus confirmed the standard model. In 1998, astronomers made the astounding discovery that the Universe was actually accelerating. This discovery implied that the Standard Model was incorrect, and had to be abandoned. This in turn, led theoreticians to come up with a model that modified the Einstein equations by adding on a term, the so-called “cosmological constant". This was very ad-hoc (no theory behind it) and amounted to nothing more than a "fudge factor". This extra term then led to the concept of "dark energy" an un-observed, unphysical (negative pressure) notion, which was generally accepted by the physics community. My talk will be concerned with the recent work of Blake Temple and myself stemming from an idea of Temple, that the anomalous acceleration of the galaxies might be due to a secondary expansion wave reflected back from the shock wave in our shock wave cosmology model. He set out with a student Zeke Vogler to numerically simulate the shock wave by a locally inertial numerical method that he and Groah derived. When Temple held The Gehring Chair at Michigan in the Fall of 2007, he invited me to join him on this project, and together we discovered a surprising new family of expansion waves that perturb the standard model, independent of the shock wave. This result led to a mathematically rigorous, non- ad-hoc, possible explanation of the accelerating Universe, based only upon the Einstein equations of general relativity.